A preferred area of application of the present invention is steering of motor vehicles, in which not only the turning angle of a steering gear shaft is to be measured, but also the forces exerted on the steering gear shaft, which act as torque. This torque can be measured as the torque angle of a torsion bar placed between two sections of the steering gear shaft. The other parameters of the torsion bar are known with this.
DE 198 34 322 A1 discloses a rotation angle and torque sensor for simultaneous measurement of torque and rotation angle of a turnable shaft. On two shaft sections a first and a second gear is placed, that turn with the assigned shaft section. The first gear meshes with a third gear that carries a magnet. A first magnetic sensor is assigned to the magnet. The second gear of the other shaft section meshes with a fourth and fifth gear, with a magnet and a magnetic sensor also assigned to these gears. The number of teeth of the fourth and fifth gears differs by at least 1, so that in a known fashion the absolute rotational angle of the shaft section can be determined, even for rotational angles greater than 360°. The number of teeth on the third and fourth gears is the same, and likewise those of the first and second gear, so that with torsion-free rotation the third and fourth gears turn synchronously. If however, torsion occurs, then between the first and second shaft sections a twisting or a torque angle appears, so that the third and fourth gears possess differing rotational settings, which can be determined by evaluating the magnetic sensors assigned to the third and fourth gears, in that a difference signal is formed from the output signals of these two sensors. Summarized in brief, the known rotation-angle and torsion sensor has five gears, three magnets and three magnetic sensors.
Similar sensors for measuring a rotational angle and/or a torque are also known from EP 1 426 750 A1 and U.S. Pat. No. 7,258,027 B2, where gears, magnets and magnetic sensors are also used.
In the sensor named initially, what is problematical is the reciprocal screening of the magnets, whose magnetic fields are allowed to only influence the assigned magnetic sensor, but not the magnet adjoining the magnetic sensor. In regard to miniaturization of such sensors, problems therefore can arise. Also, the material costs of the magnets play an important role.